1. Field of Invention
This invention relates to compositions and methods for improved microwave cooking, and particularly compositions and methods that provide fried foods in a microwave oven.
2. Description of Related Art
The use of microwave energy revolutionized food preparation and has now become common place, both in businesses and in the home. However, the advantages associated with microwave usage are tempered with compromises to food appearance, texture, flavor, and sometimes ease of preparation. In particular, although microwave energy can be used to cook foods, it lacks the ability to provide a crisping effect to the bakery or breaded/fried foods. Accordingly, a majority of uses of the microwave ovens is to reheat precooked (such as frozen) food products, rather than to cook uncooked food products in the first instance.
In the past, difficulties have been experienced in various attempts to brown or crispen food products in a microwave oven. A microwave oven heats foods differently from a conventional oven, which cooks the food entirely by radiant heat. Generally speaking, food substances are heated in proportion to their moisture content and absorption of microwave energy, which may result in considerably different heating patterns from those that exist in a conventional oven. Also, this dielectric heating by microwave radiation penetrates into most foods in a way that results in considerably different heating patterns from those that would otherwise be present in a conventional oven. In most cases, microwave energy will heat foods faster than in a conventional oven. For example, a food substance that might require 30 minutes to properly “cook” or reheat in a conventional oven, may take only 3 or 4 minutes to “cook” or reheat in a microwave oven. In a conventional oven, the oven atmosphere is heated to relatively high temperatures to transfer heat to the food surface resulting in the surface always being the hottest area in the food. In a microwave oven, the oven atmosphere is generally not heated; the food itself heats and transfers heat to the surrounding air and in some cases resulting in the outer surface of the food being cooler than the interior or having a soggy surface as the heated interior moisture and steam travel through the outer pastry layers. These differences significantly affect one's ability to brown or crispen a surface of a food product in a microwave oven as the food surface is not exposed to conventional or radiant heat.
To compensate for the microwave oven's inability to crisp and brown the surface of foods, and to prevent foods that are highly absorptive of microwave energy from being overheated, resulting in toughening and dehydration of the food, two specific “microwave active” packaging components have been developed: microwave susceptors and microwave shields.
Microwave shields are devices that do not heat appreciably in response to microwave energy, but reflect virtually all incident microwaves. Metallic foils are generally employed as microwave shields, which has the effect of shielding the food from microwave energy.
In contrast, microwave susceptors are devices that heat in response to microwave energy, converting microwave energy into thermal energy to produce radiant heat that can provide a browning and/or crisping effect to food surfaces placed in contact with the microwave susceptors. Microwave susceptors thus convert a portion of the incident microwave energy into conventional or radiant heat, which assists in cooking the food product's outer surface. Such cooking occurs by any of conduction, convection and/or radiant heating, in addition to the cooking obtained from the microwave radiation itself that has passed through the susceptor laminate. Susceptors may generally comprise almost any portion of the cooking and/or packaging surfaces, and have suitably been employed in the forms of the cooking surfaces of kitchen utensils, the bottom of packaged food products, such as unpopped popcorn, incorporated into folding cartons or trays, and a food wrap for a food product, such as meat-filled sandwiches, bread, and pastry-type products, which when cooked desirably should have a browned or crisped exterior surface.
Because of the above-described problems with browning and crisping foods in microwave ovens, the goal in the art of susceptors had been, and still is, to make the susceptor so that it generates the highest temperatures and most radiant heat possible. This goal was used because generation of the highest temperature possible also tends to mean that the cooking or heating time can be shortened, which is a primary advantage of microwave ovens. Furthermore, when a food load is close to the susceptor surface, heat can be transferred to the food as fast as it is produced by the susceptor.
Susceptors frequently comprise or are included in the packaging for food products as a convenience to the consumer, so that the consumer can simply place the product into a microwave oven without any significant preparation. As a further convenience, such packaging is customarily disposable. Thus, there is a particular need for susceptors that are economical.
However, since susceptors will be brought into contact with foods intended for human consumption, it is necessary to encapsulate the microwave interactive material within films or the like that are approved for contact with food, thus resulting in a multi-layer susceptor product. Such multi-layer products are generally known in the art, and have taken many forms. Customarily, the susceptor product comprises a base sheet such as paper, cellophane, cardboard, box board or the like, a thin layer of microwave interactive material, such as aluminum and/or other selected metals, combinations of metals, alloys and oxides, and a heat resistant barrier film overlying the thin metal layer.
The multi-layer sheet may then be die cut, folded into cartons or pressed into preformed trays or containers and/or decorated with printing to form a package into which food may be inserted by a food processor. Alternatively, the multi-layer sheet may comprise a flexible laminate, which can be formed around a food product as a wrapping material at the food processor's plant. Alternatively, susceptor laminations may be configured as a variety of flexible paper or paper board structures, such as wraps, bags, pouches, sleeves, trays, pads, discs, sleeves, patches, liners, lids, and other designs that would enable the home user and food processor to utilize susceptor materials for their own microwave suitable foods.
The barrier film is typically a polyester (PET) film, due primarily to its heat resistant properties and low cost. However, the barrier film may also be polyimide, cellulose, polyethylene nitrile and other heat resistant films. Its purpose is to provide a functional barrier between the food product and as a carrier for the susceptor metal, and sometimes also to serve as a carrier for a sealable layer to facilitate formation of a package.
The microwave interactive susceptor material is typically a metal, combinations of metals, metal alloy, metal oxide, or derivatives and/or combinations thereof, in single or multi-layer formations, but also may be ceramic or carbon. Any element or compound that absorbs the electromagnetic microwave energy, either electrical and/or magnetic wave forms, and converts it to radiant heat is suitable. The metals are usually applied by using evaporative, sputtering, or electron-beam deposition methods. The metals may also be applied using such suitable methods as printing or gravure processes, and combinations of pre-selected designs of shielding and susceptor patterns and designs can be manufactured by controlled acid etching. Flakes and slurries of susceptor materials, which may be controlled acid etched to provide variations in susceptor radiant heat, are sometimes applied in a rotary printing process. Ceramics and carbon may also be applied in a rotary printing process.
Typically, the susceptor is formed by depositing a film or layer of the microwave interactive material onto the barrier film, e.g., a web of polyester film, followed by laminating the metallized film onto a web of supporting substrate material, usually board, paper or cellulose.
Numerous variations of susceptor materials and manufacturing methods have been proposed and disclosed in the art. For example, various susceptor designs are disclosed in, for example, U.S. Pat. No. 4,641,005 to Seiferth, U.S. Pat. No. 5,614,259 to Yang et al., U.S. Pat. No. 5,164,562 to Huffman et al., U.S. Pat. No. 4,927,991 to Wendt et al., U.S. Pat. No. 5,124,519 to Roy et al., and U.S. Pat. No. 5,414,248 to Phillips, the entire disclosures of which are incorporated herein by reference.
However, despite the numerous approaches that have been made to susceptor materials, microwave cooking still presents a drawback that has not been adequately addressed in the art. In particular, microwave cooking still does not provide cooking results comparable to conventional cooking methods, for a wider variety of food products. For example, microwave cooking does not provide comparable results to frying for breaded goods, raw meats, raw vegetables, raw dough, and the like. Likewise, microwave cooking does not provide comparable results to conventional methods in providing crispy cooked products, that have the taste, texture, and appearance of conventionally cooked foods.
One approach in the art to address these concerns has been to provide various coating compositions, which can be applied to a food product to provide a crispy and/or colored outer appearance to the food product. For example, U.S. Pat. No. 5,227,599 to Mason et al., the entire disclosure of which is incorporated herein by reference, discloses a microwave cooking bag and method in which a food product in the bag is cooked, browned and crisped in a microwave oven.
U.S. Pat. No. 6,139,885 to Jouanneau et al., the entire disclosure of which is incorporated herein by reference, discloses a preparation of breads and bread products prepared by heating with microwaves and also to use of a susceptor-lined cooking vessel in combination with one or more microwave energy absorbing oils or fats to provide a soft texture in the bread crumb and a crisp texture in the crust of the slice of bread.
U.K. Patent Publication No. GB 2,228,662A to Schiffmann et al., the entire disclosure of which is incorporated herein by reference, discloses a method and apparatus for browning a variety of foodstuffs in a microwave oven. The browning is achieved by the combination of treating at least one surface of the food product with a coating, packaging of the product in a container having a microwave susceptor, and heating in a microwave oven.
U.S. Pat. No. 5,389,759 to Jay et al., the entire disclosure of which is incorporated herein by reference, discloses a microwave container having coated on at least part of the inner surface thereof a browning agent for transfer of a brown coloration to the surface of a food item.
U.S. Pat. No. 5,286,504 to Sheen et al., the entire disclosure of which is incorporated herein by reference, discloses a microwave cooking process for producing food with a crisp exterior and a soft, tender interior. The process includes applying an edible hydrophilic lossy susceptor to at least a portion of the surface of the food, wherein the susceptor including glycerin, sucrose ester, and chloride salt; and microwave cooking the susceptor bearing food to a provide a crisp exterior.
In a similar manner, a number of references are directed to improved methods for microwave popping of popcorn. For example, U.S. Pat. No. 6,320,172 to Watkins, the entire disclosure of which is incorporated herein by reference, discloses a microwave popcorn bag with a susceptor and cooking oil.